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fix(pwa): strip first-paint compositing layers to prevent iOS WebKit freeze #223

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Merged
jasoneplumb merged 1 commit into from
Jun 5, 2026
Merged

fix(pwa): strip first-paint compositing layers to prevent iOS WebKit freeze #223

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7 changes: 4 additions & 3 deletions index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -145,9 +145,10 @@
</head>
<body>
<div id="map"></div>
<div id="offline-banner" class="offline-banner">
<span>You are offline — cached tiles and GPS recording still work</span>
</div>
<!-- #offline-banner is created lazily by main.ts only when the app goes offline.
Keeping it out of the static HTML avoids a position:fixed+transform compositing
layer at first paint, which (with #map) contributed to the iOS-26 WKWebView
whole-page render freeze. -->
<script type="module" src="/src/main.ts"></script>
</body>
</html>
19 changes: 16 additions & 3 deletions src/main.ts
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Expand Up @@ -511,11 +511,24 @@ document.getElementById('map')?.focus();
document.body.style.zoom = '100%';

// ── Offline detection ─────────────────────────────────────────────────────────
// The banner is created lazily (not in static HTML) so it isn't a position:fixed +
// transform compositing layer at first paint — that, with #map, contributed to the
// iOS-26 WKWebView whole-page render freeze. It only ever exists once the app has
// been offline.
function updateOfflineBanner(): void {
const banner = document.getElementById('offline-banner');
if (!banner) return;
let banner = document.getElementById('offline-banner');
if (navigator.onLine) {
banner.classList.remove('visible');
banner?.classList.remove('visible');
return;
}
if (!banner) {
banner = document.createElement('div');
banner.id = 'offline-banner';
banner.className = 'offline-banner';
banner.innerHTML = '<span>You are offline — cached tiles and GPS recording still work</span>';
document.body.appendChild(banner);
// Mount hidden, then reveal next frame so the slide-in transition plays.
requestAnimationFrame(() => banner!.classList.add('visible'));
} else {
banner.classList.add('visible');
}
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9 changes: 7 additions & 2 deletions src/style.css
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Expand Up @@ -6,8 +6,13 @@

html { height: 100%; width: 100%; padding: 0; margin: 0; }
body { height: 100%; width: 100%; padding: 0; margin: 0; }
/* isolation: isolate keeps mix-blend-mode contained to the map's own stacking context. */
#map { position: absolute; top: 0; bottom: 0; right: 0; left: 0; isolation: isolate; }
/* No `isolation: isolate` here on purpose: an empty, full-screen *composited* #map
layer at first paint was a prime trigger for the iOS-26 WKWebView render freeze
(whole page never composites to screen until a reload). Containment isn't needed —
the hillshade overlay's mix-blend-mode:multiply blends against the opaque base
tiles directly beneath it regardless, and multiply against the white body behind a
full-screen map is a no-op. */
#map { position: absolute; top: 0; bottom: 0; right: 0; left: 0; }

/* Blend at the layer container so multiply composites against the base-layer sibling below. */
.hillshade-blend { mix-blend-mode: multiply; }
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